Step 1: Prepare the Gelatin

1. Pour ¼ cup cold water into a small bowl and sprinkle 1 (0.25-ounce) package unflavored gelatin over the surface.

2. Let stand for 5 minutes until softened and absorbed.

3. Tip: Ensure the water is cold to properly soften the gelatin without clumping.

Step 2: Make the Lemon Custard

1. In a medium bowl, beat 4 egg yolks, ½ cup (100 g) white sugar, ½ cup fresh lemon juice, and ½ teaspoon salt until smooth and combined.

2. Pour the mixture into the top of a double boiler over simmering water (ensure the water doesn’t touch the bottom of the top pan).

3. Cook, stirring constantly with a whisk or spoon, until the mixture thickens to a custard-like consistency, about 8–10 minutes (it should coat the back of a spoon).

4. Remove from heat, add 1 teaspoon lemon zest and the softened gelatin, and stir thoroughly until the gelatin dissolves.

5. Set aside to cool and thicken slightly, about 10–15 minutes, stirring occasionally to prevent a skin from forming.

6. Tip: Stir constantly to avoid curdling the eggs, and cool the custard to room temperature to ensure smooth folding later.

Step 3: Whip the Egg Whites

1. In a clean glass, metal, or ceramic bowl, beat 4 egg whites with an electric mixer on medium speed until foamy, about 1 minute.

2. Gradually add the remaining ½ cup (100 g) white sugar, beating on high speed until soft peaks form, about 2–3 minutes.

3. Tip: Ensure the bowl and beaters are grease-free for maximum volume, and stop at soft peaks to maintain a light, foldable texture.

Step 4: Combine and Assemble

1. Gently fold the whipped egg whites into the cooled lemon custard mixture using a spatula, mixing until no streaks remain but keeping the mixture airy.

2. Pour the chiffon filling into the 9-inch prepared graham cracker crust, smoothing the top with a spatula.

3. Tip: Fold gently in a figure-eight motion to preserve the airiness, and tap the pan lightly to remove large air bubbles.

Step 5: Chill

1. Cover the pie with plastic wrap or the crust’s lid (if provided).

2. Refrigerate for at least 2 hours, or until firm, for a sliceable texture (overnight is ideal for best results).

3. Tip: Ensure the fridge is at 40°F (4°C) or colder to properly set the filling.

Step 6: Serve

1. Remove the pie from the refrigerator and slice into 12 equal portions.

2. Optionally, garnish with sweetened whipped cream (whip ½ cup heavy cream with 1 tablespoon sugar) or other toppings.

3. Serve chilled for the best texture.

4. Tip: Use a sharp knife dipped in hot water and wiped dry for clean slices, and add garnish just before serving for a fresh look.